1. Field of the Invention
The present invention relates to a crystallite size analysis method and a crystallite size analysis apparatus for sampling intensity data of a diffraction beam exiting or being generated from a powder sample when the sample is irradiated with an x-ray beam, and determining, based on the diffraction beam intensity data, the size of crystallites included in the powder sample.
2. Description of the Related Art
The crystallite size of crystals contained in a substance is an important factor that has an effect on the characteristics of the substance. For example, the crystallite size sometimes has an effect on drug characteristics such as degradability, fluidity, and stability. Analytical methods based on x-ray diffraction line-broadening analysis are conventionally known as methods for analyzing the size of crystallites.
When a sample prepared from a substance that is a diffraction target is irradiated with an x-ray beam, a diffraction beam is commonly generated from the sample if designated diffraction conditions, such as the Bragg diffraction conditions, are satisfied between the x-ray beam and the sample.
As is schematically shown in FIG. 11, when a diffraction beam R2 is generated from a sample S, the diffraction beam R2 escapes from the sample S at an angle 2θ that is twice the incidence angle θ of the incident x-ray beam R1 relative to an extension line drawn to the opposite side of the sample, where θ is the incidence angle of the x-ray beam R1 that strikes the sample S in relation to the sample S. The angle 2θ of the diffraction beam R2 to the corresponding incident x-ray beam R1 is referred to as the diffraction angle 2θ.
In a common x-ray diffraction measurement, the x-ray incidence angle θ is continuously or intermittently varied at a designated angular velocity, and the angle at which the sample is perceived by an x-ray detector is varied at the same angular velocity as the incidence angle θ. In the process, the diffraction beam emitted by the sample S at a diffraction angle 2θ is detected by the x-ray detector. The intensity of the diffraction beam detected by the x-ray detector in this manner is plotted as a diffraction beam diagram or diffraction beam profile P on a system of coordinates having the diffraction angle 2θ and diffraction beam intensity I as orthogonal axes, as shown in FIG. 12, for example.
It is known that the width W (see FIG. 13) of each diffraction peak in the diffraction beam profile P does not remain constant all the time but varies in accordance with the size of the crystallites that form the sample S. Specifically, it is believed that the peak width W of a diffraction beam increases with smaller crystallites, and decreases with larger crystallites.
The method for analyzing the crystallite size based on the aforementioned x-ray diffraction line-broadening analysis is an analysis method for evaluating the crystallite size on the basis of the size of the diffraction beam peak width in such a diffraction beam profile. More specifically, the crystallite size D can be calculated usingD=Kλ/β cos θ,where λ is the wavelength of the x-ray beam, β is the width of the diffraction beam, θ is the Bragg angle of the diffraction beam, and K is the Scherrer constant. Here, K is a constant determined depending on the definition of the crystallite size and the width of the diffraction beam. Crystallites that are less than several micrometers in size can be evaluated when the size of the crystallites is evaluated using this conventional analysis technique, but it has so far been impossible to evaluate crystallites that are several micrometers or greater in size.